PST viewer: open an Outlook .pst without Outlook
Open the .pst from an old job, a dead Windows PC or an Outlook export on a Mac, a Chromebook or Linux. See the folder tree with how many items each folder holds, list any folder's e-mails by date, sender, subject and size, and read a message's headers and text.
The file is read on your device, a few kilobytes at a time, so a 20 GB .pst opens in seconds. It is never uploaded and never written to.
What works today (slice 1 of 3): the folder tree, each folder's item list, and each item's headers, plain-text body and stored properties. HTML and RTF bodies, recipient addresses, attachments and search come next; calendar, contact and task views, saving as .eml and .ost files after that.
What it shows
- The folder tree. Inbox, Sent Items, Calendar, Contacts, your own folders and their subfolders, each with its item count, as Outlook shows them under “Top of Personal Folders” (or “Top of Outlook data file”). Outlook's own hidden folders (search folders, views, reminders) are grouped separately.
- Every item in a folder, in a list that loads as you scroll: date received in your time zone, sender, subject, size, whether it has attachments, and what kind of item it is (e-mail, meeting request, contact, task…). Newest first; click any column name to sort by it.
- Any message, opened: from, to, cc, sent and received times, Message-ID, the plain-text body, and the Internet headers Outlook kept for received mail, which show the path the message took.
- Every stored property. An item is a list of MAPI properties. The table under each item shows all of them, so the phone numbers of a contact or the time of an appointment can be read before slice 3 lays them out.
- How much was read. The page counts every byte it reads from the file and shows the total, usually well under 1 % of a large file.
- Password-protected files. A .pst password is only a checksum Outlook compares before it opens the file. The data is not encrypted with it, so the file opens here without the password, and the page says the password is set.
What it cannot do yet
- HTML and RTF bodies. Most mail since about 2005 has an HTML body, and Outlook usually saves a plain-text copy too; that copy is what you see. A message saved only as HTML or RTF says so, and showing those bodies is slice 2.
- Attachments and recipient addresses. The list marks which messages have attachments, but listing and saving them is slice 2. So is the recipient table: for now To and Cc show the display names Outlook stored, not every address.
- Search. Searching subjects and senders across all folders is slice 2. Until then, sort a folder by subject or sender.
- Calendar, contact and task layouts, and saving a message as .eml, are slice 3. Their fields are already in each item's property table.
- .ost files. An .ost is Outlook's offline copy of an Exchange, Microsoft 365 or Outlook.com mailbox, and the mail itself is on the server. It is recognised and refused with a hint. Outlook 2013 and later write .ost files with 4 KB pages, which this page does not read.
- ANSI .pst files from Outlook 97 to 2002 (limited to 2 GB) are recognised and named, not read. Outlook can move their folders into a new Unicode .pst.
- Change the file. Nothing is written back: no message is deleted, moved or marked as read, and the .pst on your disk stays byte for byte the same.
- Repair a damaged file. If a B-tree page or block is broken, the page names the part it could not read. Outlook's own repair tool, scanpst.exe, rebuilds those structures on Windows.
Getting at a .pst
- From Outlook on Windows
- File › Open & Export › Import/Export › “Export to a file” › Outlook Data File (.pst). Pick the mailbox or one folder and tick “Include subfolders”. Archives Outlook made itself are already .pst files, usually named
archive.pst. - Where old files are
- Outlook 2010 and later keep them in
Documents\Outlook Files. Older versions usedC:\Users\you\AppData\Local\Microsoft\Outlook, a hidden folder. On a dead PC's disk, look in both. - From a former job
- IT departments often hand over a mailbox as a .pst when someone leaves, or when a Microsoft 365 account is closed. It is the whole mailbox in one file, often several gigabytes.
- On a Mac
- Outlook for Mac cannot read a .pst from Windows directly (it imports it into an account), and Apple Mail cannot read one at all. This page reads it as it is.
Useful to know about .pst files
- What is inside
- A .pst is a small database, not a folder of e-mails. It holds two B-trees of 512-byte pages: one maps each item's node ID to its data, the other maps each block ID to where the block sits in the file. Each folder, message and table is built from blocks of up to 8 KB. That is why this page can open a message by reading a few pages and blocks instead of the whole file.
- Why the bytes look scrambled
- Outlook stores data blocks with “compressible encoding” by default: each byte is swapped through a fixed 256-byte table. Older files may use “high encoding”, a table-based scramble keyed on each block's ID. Neither needs a password; Microsoft publishes both tables in its [MS-PST] specification, and this page decodes them.
- Unicode and ANSI
- Outlook 2003 introduced the Unicode .pst (version 23 in the file's header), with 64-bit offsets; Outlook caps it at 20 GB by default in Outlook 2003 and 2007 and at 50 GB from Outlook 2010. The ANSI format before it stopped at 2 GB. The page shows which one your file is.
- Size in the list
- The size is Outlook's own figure for the item with its attachments, as it would appear in Outlook's Size column, not the space the item takes in the file.